Hey together 
I tried to sync my contacts from my private nextcloud instance to my Mac Book Pro using carddav.
Configured the connection using this docs: Synchronizing with macOS — Nextcloud latest User Manual latest documentation
But after synchronization, I got only 10 contacts on the mac. Missing my other roundabout 250 contact entries from nextcloud.
Anyone having an idea?
For some devices, the service discovery is very important:
https://docs.nextcloud.com/server/stable/admin_manual/issues/general_troubleshooting.html#service-discovery
Check if that is working well on your side.
If this is already the case, please share a few more details. What version of Nextcloud are you using, when you open the client, what do you see in the logfiles of Nextcloud and your webserver (there we can hopefully see what your client tries to access and why it fails).